This is actually a necessary assumption question. I can a see where the “to be properly drawn” language threw you, but the word “must” in the question stem is critical. This is easier to see if you use subject matter that you’re familiar with:
Q. In order for you to become an attorney, which of the following must occur?
(A). You pass the bar exam.
Notice that despite the “In order for you to become an attorney” language, this is getting at a necessary condition, not a sufficient one. Passing the bar doesn’t guarantee that you’ll be an attorney, but failing it guarantees that you won’t.
Similarly, if the product is going to be safe (at least on the questionable argument’s reasoning), that 25-can limit can’t be hit.
You’re correct in observing that the question is flawed apart from that (or, in more parallel language), it embodies a second necessary assumption – that something carcinogenic for mice is also carcinogenic for humans in the same relative quantity. But the presence of a second necessary assumption doesn’t change the fact that the one the answer choices give you is also a necessary assumption. Hope this helps.
Notice that in the similarly worded sufficient assumption questions, the wording is typically something like, “Which of the following, if assumed, allows the conclusion to be properly drawn.” There’s no “must.” That “must” is like requires, or depends – it’s necessary assumption language.